The present invention refers to a chip-type HF magnetic-coil arrangement comprising an annular magnetic core, which is embedded in plastic material, and at least one winding, which extends through the magnetic core and which consists of at least one turn, the turns being composed of conductor elements extending parallel to the end face of the magnetic core and of conductor elements extending parallel to the axis of the magnetic core and embedded in embedding plastics.
The present invention additionally refers to methods of producing such HF magnetic-coil arrangements.
The increasing degree of miniaturization of electric circuits, which especially resulted in surface mounted devices--SMD--including socalled "chip"-type components, leads to the wish to produce also HF magnetic-coil arrangements, such as toroidal core transformers, inductors provided with magnetic cores, transformers, coils and the like, as chip-type components having very small dimensions. However, annular magnetic cores having an outer diameter of less than 6.3 mm and, accordingly, an inner diameter of the hole of less than 2 mm are practically no longer suitable for winding by means of an automatic winding machine. Although, in the case of an inner diameter of the hole of 2 mm, winding by hand is still possible, such winding is out of the question for large numbers of pieces because it is too expensive and, moreover, it does not result in the demanded close tolerances of the electric values. The winding shapes, which cannot precisely be observed in the case of this type of winding operation, will not only cause deviations as far as the inductance values are concerned but they will also result in a very large spread of the capacitance values.
U.S. Pat. No. 4,536,733 describes an HF transformer, which is provided with an annular core of ferrite material used for supplying energy and one winding of which consists of wire wound on the annular core, whereas the other winding consists of individual sheet-metal components having an adequate shape and providing, together with printed conductors on a circuit board, the turns of the winding. This type of embodiment is not applicable to the present invention.
JP-AS 1-278707, published in Patents Abstract of Japan, E-882, Jan. 31, 1990, Vol.14/No.55, describes a chip-type induction coil and a method of producing the same. This method includes the steps of producing at least two parallel rows of holes in a flat body of magnetic material. Between these rows of holes, conductors, which are arranged on the upper flat side of said body such that they extend parallel to one another and at right angles to the peripheral sides and on the lower flat side of said body again such that they extend parallel to one another, but at an acute angle to said peripheral sides, i.e. at an oblique angle above this flat side, are formed in such a way that they extend helically around the body and border on two respective holes on the lower flat side. The holes are metallized at their inner surfaces so that a circuit in the form of a coil is obtained. This structural design and this production method differ fundamentally from those according to the present invention because the conductors are applied directly to the body of magnetic material and because the body does not have an annular shape.
U.S. Pat. No. 3,477,051 describes a chip-type magnetic-coil arrangement comprising an annular magnetic core, which is embedded in plastic material, and at least one winding, which extends through the magnetic core and which consists of at least one turn, the turns being composed of conductor elements extending parallel to the end face of the magnetic core and of conductor elements extending parallel to the axis of the magnetic core and embedded in embedding plastics. In the case of this magnetic-coil arrangement, the embedding plastic is produced by injection molding around the whole annular core, i.e. on both end faces as well as on the circumferential surface and on the inner surface of the interior of the annular core, in one working cycle. In the course of this working cycle, the embedding plastic has simultaneously formed therein grooves in such a way that these grooves extend helically around the annular core according to the coil desired. Subsequently, these grooves will be filled with metal or their surfaces will be metallized so that a magnetic component will be obtained, which is provided with at least one winding consisting of turns. This component will then be attached to a carrier body or inserted into recesses of a carrier body having the shape of the chip with adequate connection and contact areas having electrically connected thereto the ends of the at least one winding.
U.S. Pat. No. 3,486,149 describes an improved production of the above-described magnetic-coil arrangement. The working cycle in the course of which plastic material is formed around the annular magnetic core includes, on the one hand, the step of enclosing this core by a body of plastic material provided with recesses for the turns of the coil and, on the other hand, also the step of producing a housing, which, in the course of this working cycle, is also provided with adequate recesses for conductors leading to connection areas as well as with plated-through holes. The housing preferably has a rectangular and flat structural design and one of its narrow lateral surfaces is provided with pins for insertion into holes of printed circuits. Hence, the component produced is not a chip-type component.
In contrast to the present invention, the magnetic-coil arrangements described in these two U.S. patent specifications include as conductor elements, at least on the two end faces and in the interior of the core, grooves, which are metallized on their inner surfaces and which are already produced when the envelope of plastic material is being manufactured in an enveloping work cycle by means of an adequately constructed, complicated injection molding tool; in the case of this work cycle, it will be necessary to move each magnetic core past this tool or to provide a plurality of such tools, if efficient production is to be guaranteed. Moreover, the step of filling the interior of the core with plastic material does not constitute part of the enveloping step so that this will require an additional work cycle, if, e.g. for reasons of insulation, the interior or also all conductors are to be covered with plastic material. However, the HF solenoid arrangement according to the present invention differs from the known embodiments especially with regard to the fact that the conductors provided on the end faces are not arranged in grooves, but on the surfaces, and that the electric connections interconnecting the conductors of the two end faces are provided in holes outside and inside of the core. The advantages resulting therefrom with regard to the structural design and the production process will be explained within the framework of the description of the present invention.